As an existent linear moving device of this type, a linear guide device comprising, for example, as shown in FIG. 9, a guide rail (guide shaft) 1 extending longitudinally in an axial direction and a slider (movable member) 2 movably mounted overriding the guide rail has been known.
Rolling element rolling grooves 3 extending axially are formed on both lateral sides of the guide rail 1, respectively, and a slider main body 2A of the slider 2 has rolling element rolling grooves (not illustrated) formed to the inner lateral surfaces of both sleeves 4 being opposed to the rolling element rolling grooves 3, respectively.
Then, a plurality of steel balls as rolling elements are loaded rotationally between both of the opposed rolling element rolling grooves, and the slider 2 can be moved axially on the guide rail 1 by way of the rolling movement of the steel balls. Along with the movement, the steel balls put between the guide rail 1 and the slider 2 conduct rolling movement and move to the end of the slider main body 2A of the slider 2 and, in order to axially move the slider 2 continuously, the steel balls have to be circulated endlessly.
Then, linear rolling element channels (not illustrated) penetrating in the axial direction are further formed in the sleeves 4 of the slider main body 2A, end caps 5 are formed on both front and rear ends of the slider main body 2A and rolling element circulation R portions 6 curved in a semi-arcuate shape communicating both of the rolling element rolling grooves and the linear rolling element channels (refer to FIG. 10) are formed to the end caps 5, to constitute a rolling element endless circulation tracks 7.
Further, as shown in FIG. 10, between each of the steel balls B adjacent with each other in the rolling element endless circulation track 7, a retaining piece 9 having concaved surfaces 8 on both lateral surfaces opposing to the steel balls B is formed such that it is in contact at the concaved surfaces 8 with the steel ball B. It has been proposed, for example, as shown in Japanese Unexamined Patent Application No. 2000-120825, a retaining piece that does not reduce the load capacity and the rigidity even in a case where the spacer (retaining piece) is disposed between loaded balls and that can decrease friction between the loaded ball and the spacer to improve the circularity of the spacer.
However, in the existent retaining piece, since the rolling element endless circulation track 7 comprises a linear rolling element channel and a curved rolling element circulation R portion 6, and the rigidity value of the retaining piece is large as well, a difference is caused between a minute moving amount dx1 of a steel ball that moves finely from the linear rolling element channel on the loaded side to the curved rolling element circulation R portion 6 on the non-loaded side, and a minute moving amount dx2 of a steel ball that moves finely from the curved rolling element circulation R portion 6 on the non-loaded side to the linear rolling element channel on the loaded side, corresponding to the minute moving amount dx1 in view of a geometrical relation, to result in problems that the difference causes zig-zag phenomenon or fluctuation in the dynamic friction of the steel balls to hinder the smooth revolutional movement of the steel ball (motion along the circulation channel) making it difficult to improve the operability further.
In view of the above, for further improvement of the operability and the low noise property by the adsorption of difference between the minute moving amount dx1 and the minute moving among dx2, the present applicants previously proposed the specification of Japanese Patent Application No. 2000-203324 in which it is described that a retaining piece is provided with resiliency and that the rigidity value is preferably 0.053 N/μm or more and 0.175 N/μm or less in view of the operability and the endurance.
However, in a case of using an elastomeric material such as HIGHTREL or PERPREN (trade name of products manufactured by Toyo Boseki Co.) in order to obtain the above described value for the retaining piece easily and at a reduced cost, the retaining piece is swollen with oil and fats such as lubricants to greatly fluctuate the pitch between steel balls depending on the position of contact between the steel ball and the retaining piece. Then, the fluctuation may possibly change the amount of gap in a series of row of rolling elements (comprising rolling elements and retaining pieces put between the rolling elements) that circulate through the rolling element endless circulation track 7 to result in problems of giving undesired effects on the operability and the low noise property and also giving undesired effects on the durability in a case where the change of the gap amount is remarkable.
The present invention has been accomplished in order to overcome such disadvantages and it is an object thereof to provide a linear moving device capable of suppressing the fluctuation of a pitch between rolling elements due to the effect of swelling caused by oil and fats such as lubricants also in a case of using an elastomeric material for the material of the retaining piece thereby providing a further improvement for the operability, low noise property and durability at a reduced cost and easily.